The "True Cost" of Batteries?

[safe]

For demonstration purposes these are the basic "units" of batteries and prices that are available today for the different types:

 

[safe]

Then for our "test case" we assemble a theoretical 36V 30 Ah battery pack not worrying about logistics, but just to compare battery technologies:

 

[safe]

So what seems apparent is that NiCad are not "competitive" to the ratios that the other technologies provide. On a "cost effectiveness" basis NiCad is not in the running. Now the number of recharges factor probably assists the NiCad in bringing it back in line, but otherwise I don't see it's value.

Observations?

Comments?

 

[safe]

And I think the "true cost" of Lithium is actually much higher than the battery cost alone. You still need the PCB circuits that can get rather expensive so you have to tack that on to the price. And the "fear factor" of a potential problem with meltdown is like having a nuclear reactor in your garage.

NiMh "seems" to offer a very competitive "price point" between SLA and Lithium. It "seems" to offer more than the NiCads and the weight is low enough that you can still get some good performance out of it.

So unless your weight needs are "extreme" the most "cost effective" battery technology today appears to be NiMh...

 

[patrick_mahoney]

NiCd's have very high discharge rates. If you want to pull 50C from a pack, you can't with either lithium ion or NiMH. So NiCd's aren't completely out of the running - they are just relegated to a niche application.

A bit of a quibble with your prices.

As of this morning (in quantities >101)
batteryspace.com
10Ah 1.2V NiMH $5.40 each.
2Ah 3.6V Li-ion 18650 $3.96 each.

all-battery.com
10Ah 1.2V NiMH $5.35 each
2.2Ah 3.6V Li-ion 18650 $4.39 each

Taking the better of these two numbers (NiMH from batteryspace, li-ion from all-battery), tightens the gap a bit. The theoretical NiMH pack is now $482 and the theoretical li-ion pack (using a cell count of 146 to count for 10% capacity reduction) is $578. But this not entirely fair since the quantities are >101 to get that price, but the NiMH is only 90 cells ($5.70 each) so then it becomes $513 for NiMH.

Where did you find 10Ah NiMH for $4.75?


I did this activity last summer when I was trying to choose between NiMh and li-ion batteries for my e-bike. I ran the numbers, looked at costs, and looked at my pre-existing battery chargers and opted for the 18650 route. One of the things that made me go with lithium ion was that I already had a really good lithium ion charger and I couldn't figure out how I was going to charge a really large NiMh series and parallel NiMH pack - particularly how it would work with the parallel chains.

The biggest problem with lithium ion batteries in my mind is the limited charge/discharge cycles and the long-term capacity reduction due to oxidation. So you spend a lot of money and you have a pack that has half the capacity in 3 years and is esssentially useless.

 

[safe]

Where did you find 10Ah NiMH for $4.75?

http://www.batteryjunction.com/1dni10reba.html

I was planning on getting 128 just to get the better price, but the last 8 will just be "spares". (I'm planning a 48 Volt 30 Amp system)

Did you build PCB's into your Lithium pack?

If so, how much did that add to the cost? (which becomes useless in three years)

 

[xyster]

The 36v 30ah nicad can be had for $600:
http://ebikes.ca/store/

36V 5Ah NiCad, 3C Max Rate
4.1 kg (9.04 lbs)
$100.00

and can be expected to last 2-4 times as many cycles as the NiMH:
http://www.batteryuniversity.com/parttwo-36.htm

In terms of life cycling, standard nickel Cadmium is the most enduring battery. Figure 1 illustrates the capacity, internal resistance and self-discharge of a 7.2V, 900mA nickel-cadmium battery with standard cells. Due to time constraints, the test was terminated after 2300 cycles

http://www.batteryuniversity.com/parttwo-36.htm

Figure 3 examines nickel-metal-hydride. We observe good performance at first but past 300-cycles, the readings starts to deteriorate rapidly. One can observe the swift increase in internal resistance and self-discharge after cycle count 700.

 

[patrick_mahoney]

Thanks for the link to the d-cell for $4.75. That's an impressive price.


I did not build safety circuitry into my lithium ion pack - I have a thermometer built in, and a couple of fuses and that's it.

My pack is a 12s8p 18650 2.2Ah lithium pack when discharging. For charging, I have a couple of plugs that turn it into an 6s12p pack for charging. Then I use a balancer with a battery voltage monitor for charging. So I offload the safety circuitry to the charger - which also lets me use it with other battery packs. See the pictures below for details.

In the photo showing the battery bag, you can see a small black wire going back to the pocket... that's the thermometer. In the same photo, the black boxes on the red wires are the fuses. The original diagrams above shows 30A fuses, but I am actually using 25A fuses now.

It's notable in my mind that the safety circuitry doesn't maintain battery balance. So you spend all this money on safety circuitry and you don't have any easy way to implement charge balancing across the pack.

For overcharging, I use Hyperion LBA10 balancer which monitors each sub-pack for overvoltage.
For balancing, the LBA10 keeps all of the sub-packs within +/-5mV of each other.
For excessive discharge rate, I have the 25A fuses.
For overdischarge, I have a Hyperion E-meter monitoring the voltage and current discharge (and total amount discharged).
For over-temperature I have a simple old Radio Shack wired thermometer with a temperature alarm, that monitors max (and min) temperature of inside and outside the pack. The probe is buried inside.
And, in case of fire, I have three 50lb bags of sand nearby, and I'm charging in a bricked area on the concrete floor of my garage with nothing within 8 ft on any side (I charge in the garage now - not on the wood floor of my basement).

The specifications:
The pack is 44.4V nominal, 50.4V fully-charged.
It's 17.6Ah - (16.6Ah measured).
It weighs 9.8lbs and fits in a Wilderness 36V 7Ah battery bag with room to spare (11 1/4" long X 3" high X 7" wide)).
Internal resistance is 22.5mohms (calculated)
In use, the temperature has never exceeded >4 Celsius above ambient.
I generally pull 12A out of it - 20A peak - which is about 0.7C (1.2C peak) which is well within spec. Voltage droop at max discharge when fully charged is approximately 2.5V at 20A (from memory, but I can look it up if someone cares).
At max charge rate (8A), I can charge it from empty to full in about 4.5 hours.
I have approximately 45 cycles on it so far. For longevity, I have been charging to approximately 90% fully charged - not 100%.

 

[safe]

...and can be expected to last 2-4 times as many cycles as the NiMH

After the price discount (on used or excess
inventory) and the extra runtime (compared
to NiMh from a few years ago I think, because
they are claiming to have improved the quality
of the NiMh product recently) you roughly
balance out what you get with NiMh.

NiCad is starting with a SEVERE disadvantage.

Even with all those correcting factors you're
still (at best) breaking even with NiMh.

Look at the numbers, NiCad is running a factor
of two or three behind NiMh... so it takes a lot
to catch up to that.

Note: The "equivalent" energy price is $475 and
that's not addressing the issue of weight. So for
the same price ($475) you get a battery that is
going to weigh more.

 

[safe]

I did not build safety circuitry into my lithium ion pack - I have a thermometer built in, and...

Do you have a rough idea what you paid in total?

P.S: If you could shrink the size of those images and resubmit
them you could get the column width back to normal. I've done
that before, big images aren't automatically scaled to fit, so you
need to do it yourself.

 

[xyster]

After the price discount (on used or excess
inventory) and the extra runtime (compared
to NiMh from a few years ago I think, because
they are claiming to have improved the quality
of the NiMh product recently) you roughly
balance out what you get with NiMh.

Maybe so. Where's some evidence of NiMH's supposed improved cycle life though?

At any rate (pun intended , I'm happy with my $3, 270 lithium 18650 batteries, and am planning to add more to the 18s15p pack soon. At their present rate of capacity loss, and after I damaged some from overdischarge, I calculated 4 years until the pack is at half its original 33ah capacity. As I ride everyday, that's at least the longevity I'd have expected to see from much heavier and more expensive nickel batteries.

A pic of the pack charging back when it was only a wimpy 15s15p :

 

[safe]

I'm happy with my $3, 270 lithium 18650 batteries, and am planning to add more to the 18s15p pack soon.

Wow! That has to be a whole other world to have
that much power at your disposal at that weight.

I really started this electric bike project wanting
to "beat" gasoline dollar for dollar and get the
most performance I could while doing it. With
the SLA batteries I calculated that it would take
about 2000 miles to pay them off and they are
equal to about 40 cents a gallon for gas. For the
NiMh I figure it will take 10,000 miles to pay for
them and an overall cost of about 75 cents per
gallon. With gas being now down to... $1.99
a gallon for unleaded regular it's not easy to
make the argument that you are saving so much
money. So performance starts to look more
interesting as another "angle" on the electric
bike idea.

Have you calculated what your costs are
compared to gasoline?

 

[NickF23]

You might find the following metrics helpful. The US advanced battery consortium (USABC) use the first as way of assesing the cost of batteries.

Dollars per Kilowatt hour of installed capicity. In otherwords the capital cost. For example SLA from you figures has a cost of $126 dollars per 1.080 KWH of capicity or a cost of $116 per KWH.

Nicad, using Xysters figures comes out at $555 per KWH

Nimh high rate cells at ebikes.ca comes out at $888 per KWH

Lithium maganese phosphate (LMP) I've seen for roughly $1000 per KWH

Lithium spinal titanate (altair/pheonix- unavailable but added for fun) $400 per KWH

The other useful metric is cost per KWH of delivered energy.

Therefore we divide the dollar cost by the number of KWH hours the battery actually gives over its life. To get this figure multiply the rated capacity by the cycle life at a specific depth of discharge. Whilst also remembering the peukert effect.


So for SLA delivers: (assuming 1/3 of the energy lost to peukurt and a 80% depth of discharge and 150 cycles) 79.2 KWH of energy at a cost of $116 dollars or

$1.46 per KWH of delivered energy.

Nicad (assuming 1000 cycles, no peukert at 80% DOD) gives 800 KWH of energy and costs

$1.33 per KWH of deliverd energy

Nimh (assuming 500 cycles, no peukurt at 80% DOD) costs

$2.22 per KWH of delivered.

Lithium (LMP) (assuming 2000 cycles, no peukert at 80% DOD) gives 1600 KWH of energy and costs

$0.63 per KWH of deliverd energy.


Lithium (Altair) (they claim 20,000 cycles, no peukert at 80% DOD) cost


$0.025 per KWH of deliverd energy.



As always take all battery stats with a very large spoonful of salt :wink:

 

[safe]

You guys seem to be using numbers for NiMh that
are waaaay too high. The price of NiMh has dropped
to equal that of NiCad which holds only half the energy.
So in the best scenario I can envision the prices of
NiCad and NiMh are at best equal.

What we need is to ESTABLISH the "true base price"
of each type of battery.

You can find prices that are 2-3 times the base price
if you go to the wrong place. (and "special offers" of
used or "excess" inventory shouldn't count because
those might be due to bankruptcy or something)

Run your calculations on this battery:

http://www.batteryjunction.com/1dni10reba.html

(assume your 500 charge cycle number, though they
now claim 1000 charges and also take the $4.75 price)

From the corporate site:

http://www.tenergybattery.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=32&category_id=1&manufacturer_id=0&option=com_virtuemart&Itemid=27&vmcchk=1

High quality D size 10,000 mAh high capacity nickel hydride
metal (Ni-MH) rechargeable batteries
Ultra long running time with this 10,000 mAh high capacity
Very long life time and can be recharged up to 1000 times.
Can provide over $1000 savings over the life time of this
rechargeable batteries by eliminating the need to buy hundreds
of;D-size Alkaline; batteries which cost $2.50 a piece.
Exact replacement for standard D size batteries and NiC
rechargeable batteries
Convenient operation due to that advantage that Ni-MH
batteries have no memory effect.
Can be charged anytime
Can be rapidly charged with smart chargers and universal
chargers
6 months warranty.
Battery tested based on International Electronic Commission
(IEC) standard to ensure capacity, quality and life time

 

[patrick_mahoney]

Do you have a rough idea what you paid in total?

I used a 15% coupon at all-battery.com and paid $281 w/ shipping for 101 cells. They kindly upgraded my cells from 2Ah to 2.2Ah for free - which was good because their description (of neither the 2Ah nor 2.2Ah cells) did not the product, so without the 10% boost I would have returned the cells.
Then I paid $20 for the battery bag. I had an LBA6 (an older balancer) which I sold for $10 less than the LBA10. (but the LBA10 is $40 new from b-p-p.com). I paid $3 for the two fuses, then less than $8 for the wiring. $4 for the big yellow molex (for balancing), and $7 for the Eflite EC3's, $4 for the Dean's Ultra's. I already had the charger - for electric model airplanes - but it's about $100 new. I also already had the Radio Shack thermeter - found it in an old box and remembering that it was somewhere in the garage. Maybe $10 for that if I had to buy one - although the wired versions are likely hard to find.

So:
$281+$20+$10+$8+$3+$4+$7+$4 = $337.

But if I didn't have the charger, the LBA6 to upgrade or the thermometer:
$337 + $30 + $10 + $100 = $477.

As I said above, part of my decision was made by the equipment that I already had - and a general level of familiarity with lithium chemistry cells - I've been flying electric model airplanes with lithium ion and lithium polymer packs for years.

I'm not sure what I would have done if I hadn't had the charger. NiMH was my second choice but I don't like dealing with parallel strings and I'm not sure how I would have charged them. I've also had poor luck with NiMH longevity with model airplanes in the past (several bad experiences), and I couldn't find a good price on them. When I did my shopping, the prices on NiMH and lipoly were basically the same. And then when I factored in the charger that I'd need... and then the weight savings with lithium ion was huge... 10 lbs for a 44V, 18Ah battery... hard to beat.

P.S: If you could shrink the size of those images and resubmit
them you could get the column width back to normal. I've done
that before, big images aren't automatically scaled to fit, so you
need to do it yourself.

I'm sorry to mess up the formatting. I tried shrinking them... it didn't seem to make a difference. If I shrink the charging set up any more, the comments will be unreadable...

I'm not sure what I'm doing wrong.

You guys seem to be using numbers for NiMh that
are waaaay too high.

All-battery.com and batteryspace.com are pretty well-known vendors. I was trying to be realistic with my pricing. And, no offense intended but simply pointing it out - your prices for lithium ion were off by more than mine were with NiMH. That batteryjunction price you posted is the best price on a name-brand, high-discharge NiMH d-cell that I've ever seen

 

[xyster]

I edited my pic down to 800 pixels width (I normally post at 800-900 pix as it seems a good fit for almost all screens these days)....

Patrick and I use the same 2.2ah lithium batteries from all-battery. I paid $3.79/per for about 300 before applying a 12% off coupon (and hosed two dozen in an "experiment" that went unfortunately awry so I have 270 on the bike All-battery recently raised their price on these I see as they dropped their 2000mah li-ion batteries:
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1643

I paid $9.49/per for 21 single-cell 1.5A chargers from batteryspace before they also raised their prices:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1231

No BMS except a 40-amp fuse, and an on-board analog voltmeter and ammeter w/shunt to watch the discharge. On long rides, I also sometimes carry my DVM (of the digital volt meter sort, not the doctor of veterinary medicine sort , stopping to check each subpack individually through its respective charging port.

Last year when planning this machine, I ran the real-life, per-mileage numbers for all the different common chemistries and sizes before I settled on these lithiums in large part because they were the cheapest (when considering pack-size, longevity, all the relevant metrics).

The 270-cell, 33ah 67-volt (nominal) battery pack weighs 28 lbs not including the wood boxes, wires, solder, glue, etc.

Here's a pic of 75 of the 270 I soldered in a 5s15p config:

 

[safe]

So are you avoiding the charging problems by having a charger for each battery more or less? (looks like with 270 batteries that's 12 or so per charger)

 

[safe]

Okay, so now I've added these new LOWER prices for the other battery types (Lithium and NiCad) and it does bring things much closer... anyone know of any prices EVEN LOWER?

 

[xyster]

Right...mostly. Like SLA, but unlike NiMH or NiCad, lithium batteries (of every type I'm aware of) charge in parallel as if one bigger battery. There's no problems with charge termination in other words. So since my pack is 18s15p, and I've got 21 chargers, you can reasonably conclude that I'm using one charger per parallel subpack (of 15 batteries) with 3 chargers left over -- or as I like to look at it: three chargers are in need of more batteries to charge so they don't feel left out

Another consideration when figuring pack life: I usually don't discharge past 50% because with 33ah on tap, I usually don't need to. I also usually charge to only 4.0 - 4.1 volts.

Tesla motors discusses these strategies on their blog:
http://www.teslamotors.com/blog1/?p=39

and says they expect five years from their 99s69p 6,831 lithium batteries pack.

 

[xyster]

Instead of per pound, I'd figure $ per mile ridden over the expected life of the pack. It's not chicken after all
When I did this prior to deciding my pack, lithium won hands down.

 

[safe]

You might find the following metrics helpful.

Dollars per Kilowatt hour of installed capicity.

The other useful metric is cost per KWH of delivered energy.

Hmmmmmmm.....

Seems to me the ratio of "weight to energy to price" is what we want to get a feel for as the "relative performance" of each type. Obviously if you take Lithium and say:

"Well gee, how much energy do we get per kg?"

...we are going to get a high number because Lithium is light. From the strictly "Cost For Energy Storage" standpoint the good old SLA battery produces (in my test case) the mandated energy requirement for only $126. All the other options are MORE expensive than SLA. But what is interesting from this analysis is that the other options are "clustering" around a factor of 4 times the price of SLA. So we can say:

"There is the price of SLA... and then there are others."

(since the pricing is radically different in the exotic varieties)

But in the real world of design we have to think about weight limitations. SLA (from my experience) can only go so far before it's lack of energy density and Peukerts Effect become like a brick wall to further advances.

So the next step is to think about the "ease of use" issues in any design that involved the "exotic" battery materials. I'd really like to do a "tube based and solderless pack" approach that minimizes the labor to assemble the battery pack.

So I've got a lot of "other issues" that effect the choice and it's not as simple as "what is the maximum energy". It's pretty clear that Lithium is the winner in the performance category.

I'm just not sure if the risks of fire are worth it.

Would I SERIOUSLY have to remove the battery pack every time I wanted to recharge it? Yuck! SLA is a no-brainer, I just ride, plug it in and wait for the "full" signal. No effort required.

 

[safe]

Like SLA, but unlike NiMH or NiCad, lithium batteries (of every type I'm aware of) charge in parallel as if one bigger battery. There's no problems with charge termination in other words.

I know that Lithium has a problem with "run away" charging that causes fires. But you are saying that Lithium seems to load balance better?

SLA is the ultimate in simplicity because it balances itself and has a very pronounced end of charge charactoristic.

I'll have to go back to the "Battery University" and take a second look at the Lithium issues. At first the idea of a fire was simply out of the question, but now I'd be willing to learn more about it because I'm definitely going to be testing other battery types for the next project...

 

[xyster]

I charge mine in the bike no probs. The chargers I use can only charge to 4.2 volts -- I'm not sure overcharge with these is even possible. And if it was, it'd take a very long time at the slow, CV trickle.

Overdischarge and fire is the big issue for me. These cells should not be run down past 3.7v resting (90% depleted) or 3.0 volts under load (because the PTC's begin popping, increasing the load to other cells until this happens....ruptured two cells, two dozen died a blistering heat death -- but no flames

 

[xyster]

For daily battery users, the cost of replacing ebike-sized SLA every 200-300 cycles (every 9-12 months) makes it more expensive than cheaper examples from the other chemistries.

Pretty cheap SLA:
http://www.electricrider.com/batteries/index.htm

(6) 12V, 12ah SLA's: $28 X 6 = $168
replacing once per year over 4 years = $672

Pretty cheap li-ion:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3070

(144) 3.7v 2ah li-ions for 18s8p 67 volt 16ah pack: $4.12 X 144 = $593.28

and should last the same 4 years if used daily to 50-70% DoD, which at 16ah lithium vs 12ah lead, should give comparable ride times.

 

[safe]

For daily battery users, the cost of replacing ebike-sized SLA every 200-300 cycles (every 9-12 months) makes it more expensive than cheaper examples from the other chemistries.

"Daily Battery Users?" - Wow, that's sounds like a "commuter" to me. That's not the image I'm going after. While the appeal of better performance is nice (a strong encouragement for Lithium) the idea of commuting is not valid for me. The idea I'm after is a "fun and sporty ride" that comes at a price that is below gasoline. (it's the idea of "fun without gasoline guilt")

SLA will last for 2-3 years if you ride on the weekends. That's a more realistic calculation.. weekends... so you need to redo those numbers with only 100 riding days per year. So the batteries should last for about 24-36 months.

The cost for SLA for 4 years is more like $300

The cost for Lithium for 4 years is like you said $600

It's still worth it if the performance is excellent on the Lithium bike...